This application claims priority of Taiwan Patent Application No.090123150 filed on Sep. 20, 2001.
The present invention relates to an apparatus for positioning and adjusting a light pipe, and more particularly, to an apparatus for positioning and adjusting a light pipe used in a digital light processing (DLP) projector.
Cathode ray tubes (CRTs) have typically been used to project onto a screen or other viewing surface. CRTs are typically large in size and low in resolution, however. Accordingly, many projectors with cathode ray tubes are becoming replaced by liquid crystal display (LCD) technologies in recent years.
In a liquid crystal display (LCD) projector, a light source emits light through a trichromatic filter. Then, the light with three primary colors (e.g., red, green, and blue) is projected onto three portions of a liquid crystal display (LCD) panel to form an image. Generally speaking, the color saturation and the color temperature created by an LCD projector are typically better than those created by a CRT projector. A transmission-type LCD panel of is, however, generally limited by its transmission ratio. Hence, the luminous efficiency of a transmission-type LCD panel is typically lower than that of a reflective type LCD panel. Further, the size and weight of the transmission-type LCD panel cannot typically be decreased due to structural limitation in the optical engine.
Recently, digital light processing (DLP) technology has become available. A detailed description of an exemplary DLP technology may be found in, for example, U.S. Pat. No. 5,658,063. DLP technology was invented by Texas Instruments Incorporated located in Dallas, Tex., United States. In contrast to the LCD projecting technology, which typically projects light through the LCD panels, the DLP projecting technology transmits lights through a trichromatic wheel that is rotated in a high speed to a DLP chip. The lights are reflected by the DLP chip and projected to a screen or display to form an image. One component of the DLP projecting technology is a semiconductor device, such as a digital micromirror device (DMD), controlled by a binary pulse modulator. Exemplary DMD devices are manufactured by Texas Instruments Incorporated.
The DMD chip, which is used as a rapid reflective digital optical switch, precisely controls the light in the projector. Regarding the DLP technology, light is reflected by micromirrors into a reflective light, and then projected to a display to form an image. The size and the weight of a DLP projector can therefore be greatly decreased. At the same time, a better luminous efficiency and a higher resolution can be provided by a DLP projector. Because the DMD can reflect light with a high fill ratio, DMD holds to potential to provide a higher luminous efficiency than other technologies. Digital light processing technology is therefore commonly used in applications needing high brightness and high resolution. In addition, the DLP technology typically has better heat dissipation capability than CRTs or flat panel displays so that it can use a light source with higher wattage without reducing the design lifetime of a DMD. Because DLP technology is typically an entirely digital design, the images produced are more stable and precise than those generated by other technologies.
In a DLP projector, a light pipe disposed between the light source and the optical engine is an important refractive optical component. The light pipe typically needs horizontal and vertical adjustment to meet requirement for the projected images. As a result, the light pipe needs a positioning and adjusting device.
Generally, a clip device and a bracket are used as positioning apparatus for the light pipe of the DLP projector. Screws are used to adjust the horizontal position and the vertical position of the light pipe. Referring to FIG. 1A, a light pipe 13 has a positioning and adjusting apparatus according to the prior art. The prior art utilizes the elasticity of clip device 11 to maintain light pipe 13 on alloy plate 121 of aluminum and magnesium of optical engine 12 so as to position light pipe 13. A screw 14 may be used to adjust the horizontal position of light pipe 13, and screw 15 may be used to adjust the vertical position of light pipe 13. Referring to FIG. 1B, because light pipe 13 is typically assembled by four pieces of glass 131, 132, 133, and 134, the surfaces of the four pieces of glass 131, 132, 133, and 134 can only bear relatively small stresses. To avoid overstressing the glass, clip device 11 positions light pipe 13 by using U-shaped brackets 16 and 17 which are attached on light pipe 13.
In the prior art, when screw 14 is used to adjust the horizontal position of the light pipe 13, U-shaped bracket 16 is deformed inward exert force to light pipe 13. The assembled light pipe 13 in the prior art is shown in FIG. 1B. In extreme cases, light pipe 13 might not sustain the side stress, potentially resulting in breakdown of side glasses 131 and 133. On the contrary, under the same condition, when screw 15 is used to adjust the vertical position of light pipe 13, the light pipe 13 needs to sustain both the upward stress and downward stress created. However, top glass 132 and bottom glass 134 are both supported by the two side glasses 131 and 133 so that light pipe 13 is not easy to break down.
While designing apparatus for positioning and adjusting in a light pipe 13 shown in FIGS. 1A and 1B, it is typically necessary to calculate the elastic force and pressure created to prevent the light pipe 13 from breaking down. The elastic force is generated by the clip device 11 and the pressure is sustained by the light pipe 13. These calculations make the design of a projector more difficult. In addition, the tolerance accuracy of the mold and the pressing stability should be controlled precisely during the manufacturing process of clip device 11 and U-shaped brackets 16 and 17. Further, the stress loaded on the side surface of light pipe 13 needs to be considered, and thermal effects to light pipe 13 is also an important issue to prevent light pipe 13 from breaking down. That is, when light passes through light pipe 13 and the temperature is over a heat-resistant value of the adhesive glue, light pipe 13 has the potential to deform or break down. In addition, U-shaped brackets 16 and 17, which are attached on the surface of light pipe 13, also may retard heat dissipation of light pipe 13 and lead to break down of heat pipe 13.
Because there are many factors to consider when designing a prior art light pipe adjustment structure, a novel approach for positioning and adjusting the light pipe is desired.
It is one aspect of the present invention to provide an apparatus for positioning and adjusting a light pipe to prevent the light pipe from deforming or breaking down. To accomplish this purpose, various embodiments of the present invention provide an apparatus for positioning and adjusting a light pipe. The light pipe is installed on a plate of an optical engine in a projector. The positioning and adjusting apparatus includes a bracket, a clip apparatus, a first adjustment screw, and a second adjustment screw. The bracket is formed by folding a metallic plate which has a first end and a second end. When the metallic plate is folded into the bracket, the first end and the second end perpendicularly press against each other to form a close space for accommodating the light pipe. The clip apparatus may then be used to position the bracket. The front end of the first adjustment screw presses against a side surface of the bracket so that the horizontal position of the light pipe is modified by adjusting the first screw. The front end of the second adjustment screw presses against a bottom surface of the bracket so that the vertical position of the light pipe is modified by adjusting the second screw.
It is an alternative aspect of the present invention to provide a positioning and adjusting apparatus whose material is easy to obtain and the manufacture of which is simple. For this purpose, the metallic plate of the present invention may be made of stainless steel.
It is an alternative aspect of the present invention to provide a positioning and adjusting apparatus which has better heat dissipation ability to prevent the light pipe from breaking down. For this purpose, the bracket further includes at least a protrusion. The protrusion contacts with each glass of the light pipe at the lateral-side surfaces. By reducing the contact area between the bracket and the light pipe, a better heat dissipation ability is provided.
These and other aspects of the present invention will become apparent after having read the following detailed description of exemplary embodiments that are illustrated in the various figures and drawings, wherein like numerals denote like components.